This invention relates generally to an apparatus for improving the accuracy and efficacy of surgical treatments and more particularly to locating a target region to be treated and tracking the motion of the target region due to respiratory and other patient motions during the treatment.
Various different treatments may accurately track the motion of a target region in order to apply the treatment to the target region. In radiation therapy and radiosurgery, for example, a tumor may be destroyed by a beam of ionizing radiation which kills the cells in the tumor. The problem is that the tumor may move during treatment, especially due to the breathing motion of the patient. Such respiratory motion is difficult to track using external sensors, since the extent and direction of the internal breathing motion of the patient cannot be seen with traditional imaging devices. The breathing and other motion of the patient means that it is more difficult to focus the radiation on the tumor which means that the treatment may be less effective and healthy tissue may be unnecessarily damaged.
To allow for adequate distribution of radiation dosage to the tumor, the radiation beam is typically moved during the treatment. For conventional systems, the beam is moved along circular arcs in space. The goal is to give a very high dose of radiation to the tumor only, while protecting surrounding healthy tissue as much as possible. Although this radio-surgery technique has been applied with dramatic success to brain tumors, the extension of this technique to tumors outside the head or neck areas remains difficult. The main reason for this difficulty has been the problem of accurate target localization (i.e., accurate tracking of the motion of the target). In particular, breathing motion and other organ and patient motion make it difficult to track the target tumor with high precision so that it is difficult to achieve the goal of providing a high dose of radiation to the tumor while protecting surrounding healthy tissue. Furthermore, conventional systems can only move the radiation beam along circular arcs in space so that irregular breathing motions cannot be easily followed since these breathing motions may not occur along the axis of the circular arcs traced by the radiation beam.
Another radiosurgery technique uses a mechanical robotic device having six degrees of freedom that targets a radiation beam as disclosed in U.S. Pat. No. 5,207,223 to Adler. The robotic device permits the radiation treatment beam to be accurately positioned to apply the treatment beam directed to the target region. A method for neurosurgical navigation is disclosed in U.S. Pat. No. 5,769,861. This method relates to finding fixed targets, such as a brain tumor, but does not address tracking the motion of a target organ, such as lung due to breathing, with respect to the skin surface, or tracking the motion of internal abdominal organs with respect to externally visible motion. A fiducial that may be implanted into the human body so that it is detectable by an imaging system is also disclosed in which the fiducial implant is implanted into the bone or organs of the human body. This fiducial implant permits internal structures of the human body to be analyzed, but does not attempt to compensate for motion of a target organ which moves throughout the respiratory cycle. Thus, it is desirable to provide an apparatus and method for compensating for respiratory and other patent motion in radiation treatment and it is to this end that the present invention is directed.